Linear drive and support for vertically movable control rods

ABSTRACT

A vertically disposed elongated cylinder includes a hydraulically actuated piston carried by a hollow piston rod which extends downwardly from the piston through friction-holding means consisting of a series of annular collet assemblies which are spring biased to holding engagement with the piston rod. A coupler for the load is operable from the upper end of the cylinder by a coupling rod extending upwardly through the piston and piston rod.

@hired Mmes Peten@ Winders [451 Mor. 2S, 11972 [54] UINIEAR DRM/E ANDSUPLPURT FOR 2,486,663 11/1949 Lovejoy 18s/67 VERTICAILLY MOVABHJECONTROL 3,009,747 1l/l96l Pitzer..... ....188/67 Rmmngg 2,808,903l0/l957 Kovac ..188/67 2.707.108 4/l955 Schottlcr l.Hi8/67 X [72]lnventor: Gordon R. Wlnders, Olney, Md.

- Primary Examlner--Edgar W. Geoghegan [73] Assignee. Diamond PowerSpeclnlty Corporation Amman! Examiner Lesne j. Paync {22} lFilcd: Aug.2l, 1970 Attorney-Harness. Dickey & Pierce [21| Appl. No.: .65,961 [57]ABSTRACT A vertically disposed elongated cylinder includes ahydrauliyns'l "Q2/sgi cally actuated Piston carried by a hollow pistonrod which en. [58] Meid 19 18 tends downwardly from the piston throughfriction-holding i l4/527f28/67 means consisting of aseries of annularcollet assemblies which are spring biased to holding engagement with thepiston rod. A coupler for the load is operable from the upper end of the[56] References Cited cylinder by a coupling rod extending upwardlythrough the UNITED STATES PATENTS Piston and Piston rod- 3,050,9438/1962 Thorel et al ,.92/23 X 7 Claims, 5 Drawing Figures FTP'AVFSW/`;T""/ y? L, /fy

7j /Zf lLlINlEAR lDRllVlE ANI) SUPPORT lFOlR VERTICALLY MOVABLE CONTROLRODS BACKGROUND OF THE INVENTION The invention aims to provide anextremely simple, compact and reliable linear hydraulic drive for usewhere the load is biased in one direction and which is so designed thatin stationary modes the load is effectively held against movement underthe influence of the bias by friction-type holding means which does notrely upon the hydraulic system in order to perform its holding function,and which incorporates improved means for connecting and disconnectingthe load and improved means for changing the frictional resistance ofthe holding means at desired times.

Other objects and advantages of the invention will become apparent uponconsideration of the present disclosure in its entirety.

BRIEF DESCRIPTION OF THE FIGURES OF DRAWING FIG. 1A is a verticaldiametric sectional view of the upper portion and FIGS. iB and 1C and 1Dare similar views of successively subjacent portions of control roddrive mechanism constructed in accordance with the present invention,and

FIG. 2 is an exploded perspective view of a pair of mating rings ofthestacked collet assembly.

DETAILED DESCRIPTION OF PREFERRED FORM OF THE INVENTION The basicmechanism comprises a cylinder concentrically positioned within and ofsubstantially smaller diameter than a tubular outer pressure-retaininghousing generally designated I2. A piston generally designated and itstubular piston rod lo are movable in the cylinder l0, and a series ofradially expandable and Contractable collet ring assemblies stacked inabutting relationship in a cascade assembly and generally designatedcoact with the piston rod to hold the same and the load connectedthereto stationary when desired.

ln the preferred construction shown, which is intended for verticalinstallation on a reactor vessel ofa pressurized watertype reactor, thehousing 12 is provided at its lower end with a coupling portion 22removably securable in sealed relation to a supporting portion 24 whichis integrated in sealed relation with the reactor vessel (not shown).The piston rod extends downwardly for connection to the load and alsoextends upwardly to engage the let-down nut 79 which is threaded on theupper end of the coupling rod 80. The cylinder space ll above the piston15 is connected to the interior of the reactor vessel via radial drilledpassages 26 in the upwardly extending portion, lo', of the piston rod16, above the piston, and a space 32 between the piston rod and couplingrod which extends downwardly to and communicates with radial holes 33extending through the wall of the piston rod to communication with apassage 34 surrounding the piston rod and extending downwardly tocommunication with the reactor vessel.

A plurality of check-type flow inhibitors mounted on the coupling rodrestrict the rate of downflow but allow relatively free upflow andventing. Each flow inhibitor consists ofa valving ring 27 spring biaseddownwardly against a shoulder on the coupling rod. The rings 27 haveclose clearance with the inner cylindrical wall of the piston rod whilethe shoulders are small enough in diameter so that they create noeffective restriction. Springs 30 hold the rings 27 against their seatswith sufficient force to prevent upward displacement of the rings due topressures resulting from normal convection, but yield when venting isrequired.

The space 40 below the piston within the cylinder l0 communicatesthrough a plurality of radial orifices 48, 49, in the wall of cylinder10 with the passage space 42 between the cylinder and the housing tubel2. At its upper end the passage space 42 connects with a port 45 in thehead portion 13 ofthe housing tube and which is equipped with anexternal fitting 46 for connection to a controlled source for feedingand withdrawing actuating fluid.

Orifices 49 in the wall of cylinder 10 are so spaced and sized as tocushion the final movement of the piston to the lower limit of itstravel. Orifices 48 are substantially unrestricted, while the lowerorifices 49 of reduced size are in a longitudinal series to provide agraduated arresting or snubbing action after the lower piston sealingring I7 passes the larger orifices 48 during the downward movement.

When the unit is installed upon a reactor of the pressurized water type,the cylinder space 1l may be subjected to a reactor pressure of theorder of 2,000 p.s.i. When the control system (not shown) calls forraising the load, pressure suffi cient to overcome the reactor pressureand the effect of gravi ty is introduced via fitting 46 and enters thecylinder space below the piston via passage area 42 and ports 48, 49,while when downward movement is called for, the pressure fluid ispermitted to escape from the space below the piston via fitting 46 at adesired rate and the reactor pressure above the piston, which greatlyexceeds the holding force of the collet stack, forces the piston down.The position of the piston and load can be accurately regulated bymetering fluid in and out of the port 45 by suitable hydraulic pressurefluid supply and controlling means of known character (not shown).

The lower portion of the cylinder l0 is attached to and supported by abushing 52 secured to the top ofa downwardly extending inner casing tube51, the cylinder, bushing 52 and tube 5l being in sealed relation toeach other. A fluid seal between tube 51 and piston rod 16 is maintainedby piston rings 61, 62. Alignment of the parts is maintained by abearing bushing 52. A coupling portion 64 secured to the lower end ofthe inner casing tube 5l is provided with bayonet lock portions 53,which holdingly interengage coacting portions S3' in the bottom couplingsection 22 of the housing tube. The lower end of coupling portion 22carries an extension tube 50 which projects into the reactor vessel, inthe preferred illustrated embodiment of the invention, and provides apassage space 54 into the reactor vessel and which communicates viaports 33 with the communication channel 32 area between the coupling rodand piston rod 16.

Resting on the bearing bushing 68 is a supporting and reaction collar 56for the stacked collet assembly 20. Each unit of the collet assemblyconsists of a pair of rings constructed as shown in FIG. 2 andconsisting of a multi-segment internal collet ring having a conic outerface and the segments of which are designated 65, and an annular matingenergizing ring 66 having a conic inner face slidably engageable withthe conic outer faces of the segments of the collet ring surroundedthereby. The interior surfaces of the segments are of the same radius asthe surface of the piston rod but the segments are slightly less than360 in total extent, so that when urged radi ally inwardly the segmentsbear against the piston rod and holding engagement occurs withoutforcing the segments together circumferentially and without forcing thesegments axially all the way into the energizer ring. A plurality ofsuch collet ring assemblies are stacked in engagement with each other,so that the end surface of each energizer ring engages the ends of thesegments of the next unit except at the upper end of the stack. In theconstruction shown, eighteen collet ring assemblies are employed,pointed upward so as to be nonself energizing in the down direction.

A helical compression spring 58 bears downwardly on the upper end of thestack and a heavier compression spring 70 beneath the stack urges itupwardly. The springs exert sufficient compressive force on the stack tocam the segments 65 inwardly against the piston rod with a predeterminedtotal pressure providing sufficient friction to hold the load immobileduring the hold mode. Spacers 7l and 72 at each end of the stack act asthrust members for the springs. Shoulders 74 and 75 are formed on theinner wall of the tube 51 to limit the travel of the rings in directionstoward the stack, The collet stack and spacer rings can shift verticallyas a unit when dragged in either direction by the friction between thepiston rod and collet stack. The lower spring 70 is proportioned toexert a preloading force on the stack which exceeds the upper springpreload by the minimum holding capacity of the collets.

During a hold mode the lower collet spacer 72 is therefore held againstthe downwardly facing bottom shoulder 75 by the bottom spring 70, andthe friction holding effect of the several stages increases from top tobottom of the stack. When the rod moves downwardly the drag of the stackmoves the bottom spacer 72 away from the bottom shoulder, and thebuildup from top to bottom is eliminated as the collet drag exceeds thelower spring load minus the upper spring load. As downward movementcontinues, the force required to move the stack increases, up to apoint, due to compression of the lower spring and relaxation of theupper spring, but since the effect of the bottom spring is equal to thefriction but less than the total of the preload effect of the upperspring plus the friction, the preload effect is eliminated and the rodcan therefore scram rapidly under the reactor vessel pressure when thepressure beneath the piston is dumped.

The gap provided by the spacing between the shoulders 74 and 75 issufficient to compensate for collet wear during the expected life of theequipment. This arrangement permits the use of a larger number of colletstages and a consequent increase in the minimum holding capacity of thestack, beyond what would otherwise be possible, while limiting themaximum drag on the rod during downward movement to a value lower thanthat which would be created by the heavy lower spring alone.

The coupling locking rod 80 extends downwardly through the completeassembly of pistons and piston rod, having a known type of grapplingportion 8l at its top, accessible from above when the plug 3l isremoved. Directly beneath the grappling portion 81 the coupling lockingrod 80 is provided with a section 82 threadably engaged with a let-downnut portion 79 rotatably positioned at the upper end of the piston rodand which when turned adjusts the vertical positioning of the couplingrod. At its lower end the coupling rod carries a projecting crosspin 83for coupling to the control rod spider 84. The crosspin 83 at the lowerend of the rod is engageable in diametrically opposed J-slots 90 in thetubular upper portion of the control rod spider 84. The lower end of theguide tube extension 50 of the piston rod 16 bears against the top ofc0ntrol rod spider portion 84, and thereby transmits the reaction of thecoupling nut 79 when the coupling rod is pulled up with pin 83 in theJ-slots. By virtue of this arrangement, when the closure plug 31 isremoved and a suitable tool is connected to the grappling portion 8l tohold it against turning while nut 79 is turned, the coupling rod 80 maybe raised or lowered as desired, and it may also be turned, by turningeffort applied to part 81, to position the pin 83 in the shorter blindlegs of the J- slots 90, which constitutes the coupled position, or,when the coupling rod is lowered and turned the control rod spider isreleased, by turning the bottom pin d3 to alignment with the longerportions of the J-slots, which are open at the upper end of the controlrod spider neck.

This detailed description of preferred form of the invention, and theaccompanying drawings, have been furnished in compliance with thestatutory requirement to set forth the best mode contemplated by theinventor of carrying out the invention. The prior portions consisting ofthe Abstract of the Disclosure and the Background of the invention" arefurnished without prejudice in an effort to comply with administrativerequirements of the Patent Office.

What is claimed is:

ll. In a linear drive including a cylinder, a piston hydraulicallyactuatable therein and a cylindrical piston rod for actuating a desiredload, means engageable with the piston rod to frictionally opposemovement of the load comprising a plurality of collet assembliessurrounding the piston rod and each consisting of a holding portionradially wedgeable against the rod and a wedging-type energizer ringmovable axially to energize and deenergize the same by exertion andrelaxation of radial wedging force on the holding portion, saidassemblies being stacked for simultaneous energization in response toaxial force on the stack, means yieldably opposing movement of the stackin each direction with the rod, comprising two spring, one reactingagainst each end of the stack.

2. linear drive as defined in claim l wherein the elastic modulus of oneof the springs substantially exceeds that of the other.

3. A linear drive as defined in claim ll wherein the piston ishydraulically biased in one direction and the energizing effort of thespring of greater modulus is exerted in the opposite direction.

4. In a linear drive as defined in claim 2, means limiting the effectiveenergizing effort of each of the springs.

5. In a linear drive as defined in claim 2, means permitting bodilyshifting movement of said stack as a unit with the rod, a thrust portionfor applying the force of each spring to the stack, and means limitingthe travel of each thrust portion in a direction toward the stack.

6. A linear drive as defined in claim 3 wherein the effective resistanceof the spring of greater modulus exceeds the frictional drag of thestack but is less than the sum of such frictional drag plus theeffective force of the other spring.

7. A linear drive as defined in claim 3 wherein all of the colletassemblies are non-self energizing when dragged in the direction of saidbias and the effective resistance of the spring of greater modulusexceeds the frictional drag of the stack in said direction but is lessthan the sum of such frictional drag plus the effective force of theother spring.

1. In a linear drive including a cylinder, a piston hydraulicallyactuatable therein and a cylindrical piston rod for actuating a desiredload, means engageable with the piston rod to frictionally opposemovement of the load comprising a plurality of collet assembliessurrounding the piston rod and each consisting of a holding portionradially wedgeable against the rod and a wedging-type energizer ringmovable axially to energize and deenergize the same by exertion andrelaxation of radial wedging force on the holding portion, saidassemblies being stacked for simultaneous energization in response toaxial force on the stack, means yieldably opposing movement of the stackin each direction with the rod, comprising two springs, one reactingagainst each end of the stack.
 2. A linear drive as defined in claim 1wherein the elastic modulus of one of the springs substantially exceedsthat of the other.
 3. A linear drive as defined in claim 1 wherein thepiston is hydraulically biased in one direction and the energizingeffort of the spring of greater modulus is exerted in the oppositedirection.
 4. In a linear drive as defined in claim 2, means limitingthe effective energizing effort of each of the springs.
 5. In a lineardrive as defined in claim 2, means permitting bodily shifting movementof said stack as a unit with the rod, a thrust portion for applying theforce of each spring to the stack, and means limiting the travel of eachthrust portion in a direction toward the stack.
 6. A linear drive asdefined in claim 3 wherein the effective resistance of the spring ofgreater modulus exceeds the frictional drag of the stack but is lessthan the sum of such frictional drag plus the effective force of theother spring.
 7. A linear drive as defined in claim 3 wherein all of thecollet assemblies are non-self energizing when dragged in the directionof said bias and the effective resistance of the spring of greatermodulus exceeds the frictional drag of the stack in said direction butis less than the sum of such frictional drag plus the effective force ofthe other spring.